The present invention relates in general to an instrument for making dental impressions and, more particularly, to a gun-like instrument which first cleans the area in which an impression is to be made with compressed air, and which then applies the impression material thereto. Still more particularly, the present invention relates to a gun-like instrument similar in a general sense to that disclosed in U.S. Pat. No. 3,530,587, issued Sept. 29, 1970, to Robert Leo Anderson, reference to which is hereby made for further background.
Dentist's impression material is prepared by mixing base and catalyst materials just prior to the time at which an impression is to be taken. Depending upon a number of minor variables, such as temperature, the particular chemicals and the amount of catalyst used, a limited amount of time is available for taking the impression. Prior to this time, a dentist has usually completed preparation of the patient for taking the impression, which involves both cleaning the area and adequately exposing the tooth at or below the gum line, as necessary, for reception of the impression material. The groove defined between the tooth and gum in this region is usually referred to as the "sulcus". In addition, it is important that each other concave and convex surface on which the impression material is to be placed be dry, because the impression material does not otherwise adhere. The presence of seepage and the physical characteristics of the impression material tend to introduce voids, bubbles, and incompletely filled areas into the impression. The more intricate the concavities and convexities, the less likely it is that these critical regions will be adequately filled.
Consequently, when a casting is to be made it is often necessary for the dentist or technician to study the matter very carefully and to interpolate, extrapolate or actually "fake" the margin line and the contours needed for the final casting. If the edges and margins of the final casting do not precisely match the prepared area of the tooth at or below the gum line, the process of decay can quickly be renewed and the useful life of the filling can be substantially shortened.
Major difficulties arise with present extrusion type impression instruments, because the impression material is flowable under pressure, but has a rubbery and elastomeric characteristic even while setting. The impression material will take the shape of something against which it is pressed, but adequate and equal pressure should be exerted on all sides to insure conformance to complex shapes. Consequently, the sulcus around the gum line of a tooth being prepared for receiving a casting cannot be filled simply by pressing an adequate amount of material toward it. Other concavities and some convex portions also will create problems unless they are precisely defined by an initial layer or film of adherent impression material.
The characteristics of the impression material can be particularly troublesome when seepage of blood or saliva occurs, as very readily happens because of the circumstances under which the impression is taken. To obtain clear access to the sulcus and the margin line which the casting base is to follow, a packing material is often used to separate the gum from the tooth in this region. Seepage begins as soon as the packing material is taken out, or can be continuous if no packing is used. The impression material will not adhere to a wet surface but instead, slips to another region. This, together with the rubbery characteristic of the impression material, contributes further to the uncertainties in the location of margins and contours which require interpolation and extrapolation to attempt to define the proper shape. It will be borne in mind that an accurate impression must be taken as expeditiously as possible, for the benefit of both the patient and the dentist. To accomplish this a versatile instrument capable of being used in different ways to overcome different problems is highly desirable but has not heretofore been available.